1. Field of the Invention
The present invention relates to a process for preparing a beanless flavor soymilk and/or okara using carbon dioxide in a state of sublimation, which avoids both chemical and thermal processing.
2. Description of the Background
For about 5,000 years soybeans and soybean products have been consumed in East Asia. A principal soybean product is soymilk, the traditional method of production of which has been to soak the beans overnight followed by washing and grinding with a specific quantity of water and then filtering the slurry product to obtain raw soymilk and the residue known as okara. The raw soymilk is then cooked for about 30 minutes and left to cool, and is then ready for consumption. Though soymilk obtained by this method has a high level of protein, it has strong beany odor and flavor; a characteristic that East Asian people are accustomed to but Westerners are not.
Despite these perceived odor and flavor problems, demand for soybean products both for human and animal consumption has greatly increased in the North American and European markets over the past 50 years, resulting in a major and modern soybean production and processing industry on both continents. According to Soya Technology Systems (1987), overall soy oil crushing accounts for 75% of world soybean consumption, which is divided between oil production (13%), animal feed (52%), food proteins (2%), plus a loss of about 8%.
Some commercial existing production processes do not include soaking as it is thought that soaking produces the beany odor and flavor that is difficult to eliminate (See U.S. Pat. No. 4,409,256.). While, some processes have been developed without using a soaking stage. A thermal treatment is mainly used in these processes to deactivate lipoxygenase, however, this has not widely used because of the low protein yield therefrom.
One approach to overcoming the problem of beany flavor has been to eliminate oxygen from the aqueous medium, as oxygen is required for undesirable lipid reactions, which are catalyzed by lipoxygenase. Some examples of these deaeration technologies and methodologies are disclosed in U.S. Pat. Nos. 4,369,198; 4,744,524; and 6,688,214.
In more detail, U.S. Pat. No. 4,369,198 describes a method for extracting ingredients of oil-containing seeds, and principally involves soybean in which soybeans are inactivated using deaerated water in an oxygen-free atmosphere. The product affords a protein yield of only 63% and the beany flavor is not completely removed.
U.S. Pat. No. 4,744,524 describes equipment for making non-beany flavor soymilk with an improvement in the deaeration system.
This patent also describes the known problem of “off-flavors” arising from the production of seed oils generally. Notably, it is well known that certain enzymes present in the soybeans and many other seeds are the major causes of off-flavor arising upon processing these seeds for foods.
Further, U.S. Pat. No. 4,744,524 describes that polyunsaturated fatty acids are catalytically oxidized by the enzymes in the presence of water and oxygen to produce hydroperoxides which finally yield the off-flavor causing volatiles. Lipoxygenase, distributed throughout the soybean cotyledons, becomes active as soon as their cell structure is broken. Therefore, the control of off-flavor has traditionally been done by inactivating the enzyme, such as by heating and/or altering pH treatments has been that tend to insolublize the soybean protein and thereby reduce soymilk yield and make it chalky in mouthfeel. The degree of enzyme inactivation required to reduce the off-flavors to acceptable level leads to an unacceptably low protein solubility. An approach of tacking the problem is to only partially inactive the enzyme, remove most remaining off-flavors by deodorization, and make any residual off-flavor by flavoring. In another approach, the enzyme is totally inactivated prior to disintegrating the beans, and the resulting insoluble soybean protein is dispersed in water by fine grinding and high pressure homogenizing. Yet another approach has been to inactivate the enzyme partially by grinding the beans in hot, pH controlled aqueous under limiting oxygen condition. Existing method of making no-beany flavor soymilk re based on the above approaches or a combination of these.
Only recently was it recognized and demonstrated that it is totally unnecessary to inactivate the enzyme, prior to or during the disintegration of soybeans, if said disintegration is carried out in an oxygen-free environment.
U.S. Pat. No. 6,688,214 describes a method for processing soybean products and an apparatus for thermal deaeration of soybean slurry. The deaeration method is combined with a thermal process to deactivate the enzymes. However, due to the fact that soybean slurry is a system of water and solids, the removal of air bubbles is extremely difficult, and it is necessary to perform the deaeration using a strong suction provided by a structurally-complicated apparatus, although air bubbles are not completely eliminated.
Further, according to U.S. Pat. No. 6,688,214, after the heating step is completed, the soybean slurry absorbs odor already generated in the soybean protein in which the thermal de-naturation is well advanced and this odor becomes fixed in the soybean slurry. This odor remains in the soybean slurry even if air bubbles are removed from the slurry that has undergone the heating step.
In the above patents, the main objective is the improvement of either apparati or methods to deaerate an aqueous-solid system, yet oxygen elimination is not achieved to a satisfactory extent. Furthermore, the apparati used are complex and consume a prohibitive amount of energy.
Another approach to overcoming the problem of beany flavor has been the use of a heat treatment to destroy lipoxygenase and the other undesirable enzymes. Although heat is effective in destroying such enzymes, these processes also decrease the protein yield because of thermal protein denaturation. U.S. Pat. No. 4,409,256 describes a thermal process to deactive enzymes from whole soybean with a yield as high as 70%, which addresses this problem to an extent.
Yet a further approach to overcoming the problem of beany flavor has been the use of chemicals, mainly for inactivating lipoxygenase. Sodium bicarbonate is used in the blanching stage, using an amount between 0.05 and 0.2% by weight. Blanching is a chemical process in which the chemical, in this instance sodium bicarbonate, reacts with and destroys enzymes. Blanching is not only used in soymilk but also in other soy products such as protein concentrates, etc. Despite its popularity, blanching is not efficient because the milk or intermediate products formed require a post-deodorization stage in most instances. However, to date no new blanching methods have been developed.
Additional processes have been developed to obtain soy products, such as soymilk, protein concentrates, insolates, and soy oil, of which some are thermal and others are chemical or a mixture of both.
Some of the conventional processes using chemicals or thermal de-activation are described below.
For example, U.S. Pat. No. 4,042,187 describes the use of a chemical (sodium bicarbonate) and thermal treatment.
U.S. Pat. No. 4,138,506 discloses some chemicals (potassium sulfite, sodium hydroxide, etc.).
U.S. Pat. No. 4,409,256 teaches a thermal de-activation of the lypoxygenase.
U.S. Pat. No. 4,744,524 employs a chemical (sodium bicarbonate) for blanching.
U.S. Pat. No. 4,915,972 employs a chemical (sodium bicarbonate) for blanching, sodium bicarbonate produces an alkali medium.
U.S. Pat. No. 5,945,151 teaches a soaking stage and vacuum cooking, which is advantageous in producing a less unpleasant soybean taste.
U.S. Pat. No. 6,316,043 describes the use of chemicals, a solidifying agent, and an acid medium, as well as a thermal stage direct high-temperature flash heating using steam, in which the soymilk needs to be homogenized.
U.S. Pat. No. 6,322,846 discloses a sophisticated mill, wherein the particles are between 10 microns and 100 microns, processed at high pressure (7000–12000 psi) using chemicals and enzymes.
U.S. Pat. No. 6,451,359 describes a complex process wherein enzymes are used to hydrolyze the proteins at high temperatures, and also uses sweeteners, flavoring, and solubilization acids.
U.S. Pat. No. 6,688,214 discloses the use of thermal, denaturation and vacuum deaeration stages but the results are unsatisfactory.
U.S. Pat. No. 4,493,854 discloses the use of supercritical carbon dioxide to extract lipids from the soybean and teaches that carbon dioxide deactivates lypoxygenase. Although this process is suitable, the extreme conditions used are problematic where the minimum pressure is 690 atm and temperature is 81° C.
Supercritical carbon dioxide is also used to extract soy oil from raw soybeans. This soy oil has acceptable levels of purpose of human consumption without significant degradation of the nutritional properties, according to U.S. Pat. No. 4,493,854. The processing conditions described are a pressure range between 793 to 855 bar and a temperature range between 81° C. and 100° C. The use of heavy-duty equipment is also required.
U.S. Pat. No. 4,495,207 discloses the use of supercritical carbon dioxide to improve defating dry-milled corm germ. Traditionally, byproducts thereof have been used as animal feed due to the problem of its bad flavor. The principal problem in developing corn germ as a finished vegetable protein product for human consumption relates to product deterioration during shipment, distribution and extended periods of storage.
Conventional pressing and solvent extraction methods using hexane or similar hydrocarbons leave lipids in the flour which either auto- or enzymatically oxidize into compounds, which contribute to grassy/beany and bitter flavors. The commercially produced, solvent-extracted, corn germ flour taught by Canoltry et al. [J. Food Sci. 42: 269(1977)], for example, contains a residual oil content of 2%. The result is an eventual and inevitable reduction in the product's organoleptic and nutritional qualities. See U.S. Pat. No. 4,495,207.
It is known that instability is relates to chalky mouthfeel which is caused by the cellulosic proteinaceous and carbohydrate constituents of the soybean. This is why commercial enzymes are used to denature the substances that produce the chalky mouthfeel and to improve the final texture of the product.
Not surprisingly, there have been more recent attempts to produce stabilized soy beverages with improved texture and taste. U.S. Pat. Nos. 6,322,846 and 6,451,359 use high pressure, chemicals, and enzymes, for example. These processes are highly industrial and complex.
Carbon dioxide is used in food processing technology. Perhaps, the best known use is decaffeination of coffee using supercritical carbon dioxide as a supercritical fluid extractor. Supercritical carbon dioxide is considered to be ideal because it is non-toxic, non-explosive, inexpensive, readily available, and easily removed from the extract product. Other traditional uses are in beverage carbonation and food presentation and storage.
The use of supercritical conditions is a problem however, because it requires heavy duty cooling equipment, with pressure being supplied by large centrifuges.
Also, a coffee decaffeination process is known that uses liquid carbon dioxide. The range of pressure used is 20 bar to about 400 bar and the temperature range is between 10° C. and about 100° C. See U.S. Pat. No. 4,472,442.
However, a need remains for a process for preparing a beanless flavor soymilk and/or okara without using thermal steps which tend to reduce protein yield and without using complex individual equipment.
A seed also remains for a process for preparing seed oils without producing off-flavors.